Mich. Comp. Laws § 42.12
The township board in each charter township may provide for and establish a police force and authorize the supervisor, or the township superintendent if one has been appointed, to appoint, subject to the approval of the said board, a township marshal and such other policemen and watchmen as may be required to protect property and preserve the public welfare and safety in that portion of the township not included within the corporate limits of any village or villages located wholly or in part within the township. No police officer of any such village shall be ineligible for appointment as a member of the township police force, except that no village police officer shall serve as township marshal. The township board shall make all necessary rules for the government of the township police force and its members and shall prescribe the powers and duties of policemen and watchmen, and may invest them with such authority as may be necessary for the preservation of quiet and order and the protection of persons and property within that part of the township not located within the corporate limits of any village.
MCL 42.12